With reference to FIG. 1 (PRIOR ART) and FIG. 2 (PRIOR ART), it is often necessary to seal a clearance gap (identified as “A”) between a housing 10 and a member 12 (ie a component) extending through an aperture 14 in the housing 10. For example, it is necessary to seal between a casing for a gear box and a power off take shaft which extends from inside the gearbox through an aperture in a wall of the casing such that another component can be coupled to the shaft. In a further example, it is necessary to seal between a machine housing and a duct which are moveable relative to one another (eg flex or relative longitudinal movement), where the duct extends from inside the housing through an aperture in a wall of the housing to form a fluid communication with a unit outside of the housing 10. FIG. 1 shows a two part housing in a dis-assembled state. A lid part 10b locates on a main body part 10a to form an enclosed housing 10, as shown in FIG. 2. The lid 10b and body 10a are joined by some suitable method at a flanges 18a, 18b provided on both parts 10a, 10b. The shaft extends from within the main body 10a of the housing 10, the details of which are not relevant to the present invention. A seal may be achieved by placing a seal member 16 between the component 12 and the aperture 14 wall to fill the clearance gap “A” between them. Any misalignment between the housing 10 and seal member 16 due to manufacture and assembly must be accommodated by the seal member 16. Failure to do so will result in reaction forces being set up between the housing 10 and component 12. Such forces will be transmitted through the seal member 16, which will cause increased wear on the seal member 16 and thus reduce its operationally effective life. Hence the clearance between the seal member 16 and the component 12 may need to be overly large (ie non optimal) to ensure the component 12 can extend freely through the aperture 14 without radially loading the seal member 16. However, to ensure optimal seal performance, there should be minimal clearance between the seal member 16 and component 12, as shown in FIG. 1 and FIG. 2.
To minimise the clearance gap “A” it is necessary to manufacture the constituent parts of the housing 10 and component 12 with very tight tolerances to ensure that misalignment between the components is minimal, and that the aperture 14 is of an acceptable size. For example, the distance between the axis of the shaft 12 and the casing 10a 10b, the aperture 14 and outer diameter of seal 16 (marked as B, C, D and E respectively in FIGS. 1 and 2) must be closely controlled. This often requires slow and/or expensive manufacturing methods, and increases the possibility of scrap and non-conformance. Additionally, current seal assembly designs contain a large number of dimensions that require tightly toleranced components, which are difficult, and hence expensive, to manufacture.
It is an object of the present invention to provide a seal assembly which can seal a clearance gap between a housing and a component extending through an aperture in the housing which can accommodate larger misalignments of the component and housing than the prior art.